High Wind in Oregon, January 8 to 9, 2019

Area Forecast Discussion
National Weather Service Medford OR
911 AM PST Tue Jan 8 2019

.UPDATE...
Maximum temperatures for today have been updated. Primary
adjustments to these temperatures were to raise them for west
side valley locations most affected by today's downslope southeast
flow and to lower them for our northern California area and areas
east of the Cascades where cooler air should pool due to general
upslope conditions and snow melt. BTL

&&

.DISCUSSION...
Low pressure with a central surface pressure of about 972MB is
present over the eastern Pacific this morning at about 42N 137W.
24 hour rainfall amounts across the coastal counties have been
appreciable, in the half inch to one inch range. Meanwhile, in
the Mount Shasta area, amounts have been .10 to .60 inches of
water. Elsewhere, amounts have been lighter, and southerly winds
have been gusty, mainly in the usual spots. Snow levels have also
risen, and the freezing level across the Cascades is between 6kft
and 6.5kft. While the freezing level is lower east of the Cascades
precipitation is not occuring there and probably will not occur
there until at least tonight.

For the remainder of today we'll be looking at more of the same
conditions as what we've experienced over the past 12 hours. Winds
will peak late this morning, come down a bit, and then another
peak is expected tonight into Wednesday morning as the cold front
finally moves inland. Precipitation rates will increase as the
front moves inland so, for now, we'll keep the flood watches out
for Siskiyou County for the combination of lower elevation snow
melt and expected heavy rainfall. BTL

&&

.AVIATION...For the 08/12Z TAFs...Deep low pressure offshore will
edge eastward today and low-level wind shear will become the main
concern, especially west of the Cascades. Along the coast,
especially north of Cape Blanco, expect LLWS to be a concern through
much of the TAF period as offshore flow limits the amount of mixing
of the stronger upper level winds. Away from the coast, upper level
winds will increase and expect some gusts, possibly exceeding 30 kt,
to mix down in the Rogue and Shasta Valleys as well as east of the
Cascades by this afternoon. Expect widespread turbulence later this
morning, continuing into tonight. Mainly VFR conditions with local
MVFR/IFR conditions in moderate rain will persist through the TAF
period. /BR-y

&&

.MARINE...Updated 845 AM PST Tuesday, 8 January 2019...A cold front
will move through the area today while a deep, broad area of low
pressure remains far offshore. This will bring a lengthy period of
southerly gales, strongest in the outer waters, and very steep, wind
driven seas through Wednesday. Long period southwest swell will
build into the waters later this afternoon into Wednesday. This will
combine with the ongoing wind driven seas to produce high surf and
treacherous bar crossings. Conditions will improve slightly under
high pressure late Thursday into Friday, but seas will likely remain
high and steep into early next week as more frontal systems make
their way into and through the region. /BR-y/Spilde

&&

.PREV DISCUSSION... /Issued 348 AM PST Tue Jan 8 2019/

DISCUSSION...08/00Z NAM/GFS/EC in.

The northern hemispheric pattern shows a wave number of five
around the globe. This is normally a progressive pattern and
initially it will be. However, a blocking high will set up over
the western U.S. around Friday and this will slow the progression
over the eastern Pacific and western U.S. through the coming
weekend. Both the EC and the GFS solutions support this scenario.

However, an active pattern is in place now and this will continue
to be the case for the near-term forecast. A long wave upper level
ridge is now breaking to the east of the area and a deep long wave
trough is moving in.

This trough will weaken considerably as it moves in, as its energy
will be sapped by a digging long wave trough farther offshore.
However, short waves ejecting from the first trough and the
trough itself will support frontal activity over the Medford CWA
until it finally moves onshore Wednesday night.

A warm front has either moved through or is moving through the
area now, and snow levels are rising up to 7000-8000 feet. The
following cold front is now moving onshore and it will be a slow
mover as it is nearly parallel to the upper level flow. The jet
streak, such as it is, is to the south, and most of the energy is
directed there. This dynamic lifting combined with orographic
lifting supports the current forecast of the heaviest
precipitation extending from Curry county southeast through
western Siskiyou county and into south central Siskiyou county now
through Wednesday. The high snow levels will create a rain on snow
scenario that may lead to flooding on smaller streams in areas
with heavy rainfall. No main stem river flooding is expected, but
they will see significant rises. Please see FFAMFR for more
details.

There will also be a prolonged period of moderate to strong winds
in the Shasta Valley and moderate winds in portions of the Rogue
valley. Unlike the last storm, the upper low will be offshore and
wind direction aloft will likely not be favorable for strong
winds to occur in the Rogue Valley. However the pressure gradient
between Medford and Redding will peak at 6-7 mb Tuesday afternoon
and remain above 5 mb Tuesday night into Wednesday. The wind
direction aloft may line up with the Rogue Valley sometimes during
this long interval, and when it does so the south end of the
valley may see Advisory level winds.

It will also be windy east of the Cascades Tuesday afternoon into
Wednesday evening with the strongest winds in the higher terrain.
At this time the winds look to be advisory level for the most
part.

A High Wind Warning is in effect for the Shasta Valley and Wind
Advisories are in effect over portions of the east side and
Jackson county. Please see PDXNPWMFR for more details.

Precipitation will diminish Wednesday night into Thursday as the
trough moves out and a long wave ridge...and low level
northeasterly flow...sets up over the area. Snow levels will drop
a bit as the precipitation wanes, but will remain above pass
levels.

Extended discussion from the Monday afternoon AFD...Friday
through Monday. The long-term will be drier than the short- term.
The storm track will shift to the south of the forecast area,
impacting primarily affecting Central and Southern California.
This is a common synoptic setup in El Nino years, which are
currently in. Deep southerly flow continues over the area, though
not likely as strong as earlier in the week. Therefore, we don't
expect major wind impacts.

Precipitation chances will continue to be focused over Northern
California and the coast and coastal mountains, though operational
models depict a mostly dry Friday and Saturday. One period of note
in the extended is Sunday, when an elongated upper trough (per the
GFS) approaches the coast and spreads light to moderate
precipitation inland. Eventually, precipitations trends southward
into California by late Sunday. Snow levels for most of this
precipitation should be higher than 5000 ft.

Fog and freezing fog will be possible in the extended, but we do
expect fog to lift relatively early because of the deep southerly
flow and lack of strong upper ridging. -NSK

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Wind Advisory from 1 PM this afternoon to 10 PM PST Wednesday
     for ORZ030-031.
     Hazardous Seas Warning until 4 PM PST Wednesday for ORZ021.
     High Surf Advisory from 4 PM this afternoon to 10 PM PST
     Wednesday for ORZ021-022.
     Wind Advisory from noon today to 4 PM PST Wednesday for ORZ026.

CA...Wind Advisory from 1 PM this afternoon to 10 PM PST Wednesday
     for CAZ085.
     Flood Watch through late Wednesday night for CAZ080>083.
     High Wind Warning until 10 PM PST Wednesday for CAZ081.
     Wind Advisory until 10 PM PST Wednesday for CAZ081.

Pacific Coastal Waters...
- Gale Warning until 4 PM PST Wednesday for PZZ350-356-370-376.
- Hazardous Seas Warning until 4 PM PST Wednesday for PZZ350-356.

BTL/MAS/JRS